Systems employing optical data storage locations include, for example, video cameras and image displays. Such systems employ an addressing structure that provides data to or retrieves data from the storage locations. One system of this type is a general purpose flat panel display, whose storage or display locations store light pattern data. A flat panel display comprises multiple display locations distributed throughout the viewing area of a display surface.
One type of flat panel display system employs a matrix-type addressing structure that accomplishes direct multiplexing of multiple liquid crystal cells that are arranged in an array and function as the display locations. Each of the liquid crystal cells is positioned between a pair of electrical conductors that selectively apply select and deselect voltage signals across the liquid crystal cell to change its optical properties and thereby change the brightness of the image it develops. A display system of this type is characterized as "passive" because no "active" electronic device cooperates with the liquid crystal cell to modify its electro-optical properties. Such a display system suffers from the disadvantage of being capable of implementation in only a low resolution display application having a limited number of addressable lines (i.e., up to about 250) of video information or data for developing a display image. Such a display system may also suffer from the disadvantages of providing limited gray scale, relatively low image contrast, and a small range of viewing angles.
Another type of flat panel display system having a matrix-type addressing structure employs an array of electrically "active" elements that act as electronic switches at each of the display locations. Such a display system may employ, for example, thin film transistors (TFT) having nonlinear signal processing characteristics that cooperate with the liquid crystal material to provide a full gray scale capability. Such a display system is capable of providing high resolution displays, good image contrast, and relatively wide range of viewing angles. A display system of this type suffers, however, from the disadvantage of being very difficult to fabricate with high production yields because of the large number of electronic elements and data drivers required in such a system. For example, a 1,000 line full color display system of this type could require up to about 3 million electronic elements and about 4,000 data drivers.
Another type of prior art display system, which is not of the flat panel type, employs a solid crystal cell and an electron beam that cooperate to form a display location addressing system. Such a display system is described in Farrayre et al., "Geometrical Resolution Improvement of Sodern Visualization System," SID 85 Digest, 266-269. Pertinent portions of the Sodern display system are discussed below with reference to FIGS. 1 and 2.
FIGS. 1 and 2 are respective cross sectional and fragmentary isometric views of a prior art display system 10 that employs an electron beam 12 of constant beam current to address particular locations on a liquid crystal display panel 13. Display panel 13 includes a solid crystal dielectric target 14 having a front surface 16 on which a single optically transparent electrode 18 is deposited. Dielectric target 14 is positioned face-to-face between an optically transparent substrate 20 and a dielectric optical mirror 22. A control grid 24 formed of closely spaced parallel wires and positioned proximally to a back surface 26 of dielectric mirror 22 receives video voltages to operate display system 10 in one of at least two possible modes.
In the preferred "potential stabilization" mode of operation, video voltages are applied between control grid 24 and single transparent electrode 18. Electron beam 12 strikes a location on dielectric mirror 22 and causes the emission therefrom of secondary electrons that function as a "local short circuit" between dielectric mirror 22 and control grid 24. The short circuit induces across dielectric target 14 a voltage that equals the video voltage applied between control grid 24 and transparent electrode 18 and thereby addresses at the location a pixel whose luminance corresponds to the video voltage.
Light rays 28 (one shown) propagate successively through first and second neutral density linear polarizers (not shown). The polarizers are positioned so that light rays 28 incident to display system 10 pass through the first polarizer, reflect off dielectric target 14, and then pass through the second polarizer. The video voltage induced across dielectric target 14 at the addressed pixel modulates the polarization of the light rays 28 that propagate through the pixel. The polarization modulation causes intensity modulation of light rays 28, which corresponds to video information.
Display system 10 cannot, however, be easily manufactured for at least three reasons. First, all video information is applied to display system 10 as video voltages between control grid 24 and the single transparent electrode 18, thereby requiring a data drive circuit having a very high signal bandwidth. Second, control grid 24 and transparent electrode 18 generate a substantial capacitance that can limit the bandwidth of such a data drive circuit. Third, writing video information on display system 10 by means of providing voltage differences between control grid 24 and transparent electrode 18 requires that control grid 24 be accurately positioned extremely close to dielectric target 14 to provide sufficiently accurate addressing sensitivities.